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- Thread starter Qcan
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- Nov 12, 2017

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I guess you just have to gather some data and find out. Like your other question, this is for statisticians and census takers, not for mathematicians. But I would expect that P(fraternal twins | birth on Dec. 25) would be about the same as P(fraternal twins), so you can probably just multiply the two probabilities (for fraternal twins and for Christmas births) together.Considering that the least amount of births in the Western World happen on December 25th, I would think the odds are a little long.

But where did you get your information about number of births?

I am asking because I have cousins that are twins that were born on Xmas day. I thought someone might have know the answer instead of going through the calculation.

I assume (if my math is correct), that without getting precise and assuming that all days had the same amount of births, that the answer would be .35 * .2740 = .0959 or 96 in every 100,000 births.

Data set is from Fivethirtyeight - https://github.com/fivethirtyeight/data/tree/master/births

- Joined
- Nov 12, 2017

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I'm not sure of your calculation; did you intentionally not convert percentages to decimals? I find that 0.2740% ignores the date; I'd expect you to have used the probability of a Christmas birth.

I am asking because I have cousins that are twins that were born on Xmas day. I thought someone might have know the answer instead of going through the calculation.

I assume (if my math is correct), that without getting precise and assuming that all days had the same amount of births, that the answer would be .35 * .2740 = .0959 or 96 in every 100,000 births.

Data set is from Fivethirtyeight - https://github.com/fivethirtyeight/data/tree/master/births

Taking your value of 0.35% of births being fraternal twins (which seems low to me, but I know it varies a lot), and the claim here that the number of births on Christmas is 0.57 of the 1/365 that would be expected, I find that the fraction of births that are fraternal twins on Christmas is 0.0035*0.57*1/365 = 5.466e-6, which means 0.55 per 100,000 births.